Control valves are often used in process control plants or systems to control the flow of process fluids. Control valves typically include a valve plug (e.g., a metal valve plug) and a valve seat (e.g., a metal seat ring) that are disposed in a fluid path to control the flow of fluid. The valve plug typically includes a valve plug tip connected to a valve plug body. An actuator moves the valve plug between an open position and a closed position at which the valve plug tip engages the valve seat to form a seal.
In severe service applications such as, for example, in the hydrocarbon, metals and mining, and petrochemical industries, control valves may be subjected to severely erosive service conditions that can rapidly wear or reduce the operating life of the valve plug. For example, the valve plug may be exposed to flowing process fluids that contain entrained particulate (e.g., ceramic catalyst fines, sand and aggregate from downhole formations, etc.) that can damage a sealing surface of a valve plug tip made of metal.
Therefore, in severe service applications, valve plug tips made of ceramic materials are often employed to reduce damage caused by severely erosive process fluids that may otherwise damage metallic valve plug tips, thereby increasing the operating life of the valve plug. Although highly resistant to the erosive and/or corrosive effects of particulate and the like, such ceramic materials may be more brittle than metallic materials. Thus, the ceramic material valve plug tips may not withstand relatively high actuator thrust forces that are often required to provide a tight fluid flow shut-off. For example, the actuator imparts a relatively high seating load or force to the valve plug when the valve plug sealingly engages the valve seat to provide a relatively tight shut-off and prevent or restrict fluid flow through the passageway of the valve for on/off applications. Under such high loads, stress concentrations in a valve plug tip made of ceramic can cause the valve plug tip to fracture, shatter or crack.